Probably a bad sending unit (in tank)
In the tank near fuel pump.
gage is the best (kon )
it is located on the fuel gage
"R" on the fuel gage means "Reserve".
The fuel gauge sending unit is located inside the fuel tank.
it should say so on the fuel gage
why does the fuel gage on 2005 mustang don't work?
The fuel gages, the battery gage, the oil pressure gage, and the coolant gage are on the upper instrument cluster?
If it just the fuel gage then your sending unit is not working or their is a broke wire between the tank and the gage. If all your gages are not working check for a blwon fuse.
the fuel pump is located in the fuel cell. the sending unit for the gage & the fuel pump are on the same bracket.
fuel gage sending unit inside the fuel tank
In most cases the fuel gauge sending unit in the fuel tank has failed.